Snow motor vehicle



It'. R. BURCH'.

sNow MOTOR' VEHICLE- APPLICATION FILED NOV. 27., |920 s. SHEETS-SHEET l.'

v :mamon E 303 l ATTORNEYS Mmm .Um Im Lil I'. R. BURCH. sIIIow IIII'IToII VEHICLE.

APPLICATION FILED NOV. 27, 1920.

IPmtntIeII 001k.. W9 R92.,

F. n. uRcH.

SNOW MOTOR VEHICLE. APPLlcAn'oN man Nov, 21. |920.

Mmm @en 1mm.,

6 SHEETS-SHEET 3.

/fzg N Y ATTURNEYS 6 SHEETS-SHEET 5 IIIIIEIIToII mic/"519W ATTRWIEYS F. R. BUHCH. SNOW MOTOR VEHICLE. APPLICATION FILED IIov. 21,

F. R. BURCH.

SNOW MOTOR VEHICLE. APPLICATION man Nov, 27, lazo.

6 SMEETSQSHEET 6.

ATTRNEVS FREDERICK R.. BEECH, OIF SEATTLE. WASHJINGTON, ASSIGNOR TO ARWSTEAD SSI'OWVl TED, 0F NEW YORK, 1\T. Y., A CORPORATION OF DELAWEE.

MOTORS, INCORPO SNOW MOTOR VEHICLE.

Application tiled November 27, 1920. Serial No. 426,788.

To all 'whom t may concern.'

Be it known that I, FREDERICK R. lBURorr,l

` ing all the essential lfeatures for meeting the peculiar and varying conditions encountered in this kind of service. A suc cessful snow motor vehicle/must travel over deep, fresh' snow falls, compacted `snow or ice, ice'crusts 'overlying soft snow, and slush, and must also accommodate itself to surface irregularities. For the sake of brevity, the material traveled over will be referred to hereinafter simply 'as snow, snow surface or snow body, except when further qualified to explain different characteristics of the machine.

in northern latitudes, where the snow fall is heavy for several months of the year, transportation by horse power and by wheeled motorA vehicles is always difficult and often impossible; and it is desired to provide a motor vehicle capable of breaking out roads or even going across country through newly fallen deep snow, and hauling trailers at the same time when necessary or desirable. This is probably the severest service required, but the vehicle should alsotbe able to cope with all other conditions of snow surface, to go backward as well as forward, to make considerable speed under'favorable conditions and exert increased tractive effort withA correspondingly reduced speedunder unfavorable conditions. v

After study of the problem, experiment, and practical tests and experience with vehicles under thevarious conditions encountered throughout northern winters` I have devised and successfully demonstrated in operation a vehicle which meets the conditions imposed. So far as l am aware, l am the first to produce a really practical motor sled incorporating all the features which are found to be essential in practice.

The complete vehicle embodies a number of essential features, as explained hereafter, but from one point of view, the primary requirement is .adequate support upon and ance and at the same time to give a reduced supporting area upon hard snow or ice, also with properA tract-ive effect upon such surfaces. l

More particularly described, the tractors consist of revoluble drums of relatively large diameter and of adequate length havin surfaces whih are curved in the plane o their axes for a great part of their length to provide for the most advantageous snow contact under varying conditions of snow texture .and surface conformation. These drums are provided with relatively shallow helical projections which have an angular reaction upon the vsnow surface when the drums are revolved-and so drive the vehicle. The vertical face area of these projections issufficient to give proper driving' impulse in soft snow, but not sufficientto create undue frictional resistance. Their peripheral surfaces serve as the principal support ofthe tractors upon, and provide adequate I driving contact with, hard snow or ice. The surface'curvature of the tractor drums in the axial plane is also such that the tractors will ride over soft snow and hard lumps satisfactorily, either forward or backward. Preferably also, one end of each drum is smooth, that is, free from helical driving ribs for a certain distance from one end (the smaller) toward the other (larger) end, to exert a channeling and smoothing e'ect upon soft snow in advance of driving contact of the ribs with the channelled snow surface. as the tractor advances withthe smooth surface foremost. each tractor unit is interrupted at a polnt Preferably also,

between its ends, that is, it consists of'two drums in axial alinement, rather than a single continuous drum, and the surface of the drums in the -planes of their axes is defined by a continuous curve, extending substantially from the front end4 of the front drum to the rear end of the rear drum; and preferably also this curve has a decreasing radius toward the'ends, so that the forward u mentioned below, enables the drums to proprected backward. Usually two such tractorerly ride over and conform to all kinds of snowlbodies and surface irregularities, as explainedin the following detail description. The drums are also preferably arranged so that the principal smooth segment of the front drum is directed forward, and the smooth portion of the rear drum is diunits are provided in parallel relation.

y In connection ith such tractor elements I provide a suitable main frame supporting a body structure, a suitable motor, and 'power transmission devices; ,and additional framing and supporting structures to connect .the tractors properly with the main frame. I have found that an essential requirement in connecting the tractors with the main frame, or as otherwise considered, in supporting the main fr ame upon the tractors, is that each tractor unit shall have a considerable oscillating or pivotal movement in its longitudinal, vertical plane in relation to the main frame, to permit each tractor unit to conform properly to irregularities of the snow surface. This requirement is provided for in the arrangement of the frame structure. The invention further provides suitable driving connections from `the motor or transmission mechanism carried by the main frame to the tractor units, and provides suitable flexible elements in such\driv ing connections to permit the oscillating movement of the tractor units and for other reasons.

It is found desirable to pivotally connect the tractor units to the main frame at an Intermediate point of the length of each tractor unit, and also to provide driving connections to the tractor shafts at points substantially coincident with their pivot-connectlons. The invention includes mutually adopted structures which provide the desired plvot and drive connections in a lsimple and desirable form.

The invention also provides suitable steering means, consisting in a preferred embodiment in forwardly arranged dirigible runners, and provides for suitably connecting these runners withthe main frame so that in an advantageous way, and so that the individual runners, and also the steering structure as a whole, have a certain flexibility of movement.

Since the vehicle frequently runs in deep snow, in which the tractor drums sink quite deeply, the frame, driving and steering connections` and other features are designed to provide an unobstructed space longitudinally through the machine between the drums, extending up a substantial distance above the level of the bottoms of the drum surfaces; and this unobstructed clearance space may be substantiall as high as the average horizontal plane o the drum shafts. Thispermits the vehicle to pass freely over a relatively high ridge formed between the channels pressed by the drums in deep, soft snow, or other obstructions straddled by the drums in the progress of the vehicle.

I' have found that springs comparable to the chassis springs of ordinary motor vehicles, such as have been proposed for motor sleds insome cases, are usually, if not always, unnecessary in connection with other features of my invention, for the reason that the flexible -mounting of the tractor units and guiding runners carries the vehicle very smoothly over snow surfaces of all sorts, without any bumps or shocks which are objectionable orinjurious either to the vehicle or to the goods or passengers carried. I, therefore, dispense with any springs having a principal cushioning or supporting function, and correspondingly simplify the frame structure.

Various strains and thrusts are imposed on the frame and on moving parts, incident to movement over various surfaces, and driving reactions. The proper resistance to, and distribution of, these stresses have been carefully provided for, in thearrangement of main and tractor frame members, driving and pivot connections, and guides for` the movable tractor frames, as explained suffciently hereafter.

'To meet the various conditions briefly suggested above, and to incorporate the structural features mentioned, `as well as others referred to later, is an exceedingly complex inventive problem.' In its solution practically Iall the principal parts of. the machine have had to be mutually adapted to each other. These features of mutuall adaptation will be sufficiently understood from the following detail description of a representative form of the invention.

The invention comprises numerous other features which are best described in connection with a detailed description of the accompanying drawing, which shows one exemplifying embodiment of the invention.

After considering this it will be understood 'that numerous subordinate parts or sub-combinations of-elements of the invention have .,tical section at 4-4, Figure 2;

Figure l5 is a perspective view,` somewhat diagrammatic, of the frame structure;

Fig re 6 is an enlarged longitudinal sec--4 tion of a tractor drum;

Figure 7 is a detail, partly in section, of

one of the pivotal tractor carriers and part of another one, and the adjacent part of the ymain frame Figure 8 is a sectional detail in the plane. 8 8, Figure 7 ,l f

Figure'9 is an enlarged side elevation of 'the front end .of the machine, showing the steering runners;

Figures 10 and 11 are small diagrammatic side elevations of the vehicle, showing thejaccommodation of the tractors and runners to diferent snowI surface conformations, and

Figure 12 is an enlarged fragmentary sectional detail of one of the tractor drums.

Figure 13 is -an enlarged sectional detail of one tractor shaft, with parts broken away, showing mainly the shaft, bearings and lateral guide means. l Figure 14 is an enlarged fragmentary rearI end elevation, partly in section, of one of the vertical shaft-guides.-

` The general organization of the machinel is best explained by first considering Figure 5, .in connection with Figures 1, 2, 3, 4 and 9; A frame stucture F, of generally rectangular plan, carries the vehicle body B. This frame F is analogous to the chassis frame of an ordinary motor vehicle and serves conveniently to support the motor M, chan -speed gearing contained in the gear box and a clutch contained in the intermediate clutch housing C,'and these parts may conveniently be, as shown, of so-called unit power-plant construction, as now employed in the majority of motor vehicles, or any other suitable arrangement -of the motor, clutch and change-speed gearing may be made. The main frame also carries suitable control devices, of which `gear-shift lever lL is a sufficient example. Transversely arranged below the chassis .frame F and rigidly connected to it by brackets 1 is a beam 2 having downwardly curved ends 3. Below beamv2 and substantially in thelongitudinal center of the machine is a beam 4 which extends substanially throughout the length of the vehicle. strut 5 rigidly connects the center of beam 2 with an intermediate part of'beam 4. Beams 2 and 4 may be of any suitable structural section but are vconveniently of lI-section as shown. Near the, front end ofthe frame F each of its side members is provided with a bracket 6 and each of these brackets carries a vertical guide 7 for the front end of one of the tractor frames. Near the rear end of the frame F each of its side members is provided with a bracket 8 and each of these brackets carries a vertical guide 9 for the rear end of one of the tractor frames. Transverse frame members 10 connect guides 7 to longitudinal beam 4 and similar frame members 11 connect guides 9 to beam 4 near its rear end. Frame members 10 and 11 constitute, in eHect, continuous cross braces for the lower front and rear portions ofthe rigid frame structure. Near the front end of frame F diagonal braces l()a connect side members of frame F with beam 4 and usually this last connection is substantially at the point of connection between cross members 10 and beam 4.

At each side of the rigid frame is a tractor frame T. Each of these comprisesa longitudinal beam or truss 12, generally of a curved orarched form., as shown, with downwardly bent front and rear'ends 13 and 14, respectively, and a transverse member or yoke 15, and these members areconnected by braces 16. Preferably these braces are arranged as best shown in Figures 4 and 5 at downwardly divergent angle to each other, so that they meet atl 16a where they are connected by means of a suitable bracket to truss 12 and the lower ends of the braces are connected at the widely separated points 16b and 16c to the side member of'yoke 46. This arrangement gives a triangular bracing of the tractor frame adjacent to its drive mechanism and renders the frame very strong and stiff, both vertically and laterally. Each of the okes 15 may be of substantially rectangu ar form (in plan)`wand its side members are provided with bearings 1 7 through which passes a shaft` 18 which is the tractor drum carrying and driving shaftl of the tractor unit. The ends of truss 12 are provided with bearings 19 and 20, through which shaft 18 also passes. The outer end of eac-h of the yokes 15 `is provided with `a trunnion bearing 21, through which asses a trunnion 2 2, conveniently in the form of abolt carried by' a clevis 23 fixed to the adjacent end 1 of beam 2. The inner end of each of yokes 15 has a trunnion bearing 24 (Figures 4, 8 and 9) through which passes a trunnion 25, conveniently in lthe form of a bolt which extends through a suitable socket formed in beam 4 or provided in plates 26 bolted to the beam. The trunnion bolt is secured by nuts 27. Bolt 25 thus serves .as a -trunnion for the inner ends of both of yokes 15, and the heads, consistingof nuts 27, resist lateraldisplacement of the yokes. Eachof the tractor yokes 15 is preferably. provided 4with two arms 140, one bolted to leachy side member af the yoke. These arms'lterminate iin-'flanges 141, whose inner faces bear against plates 142, securedto the web of beam 4. Clips 143 are also secured -tothe beam andthese clips have ends 144 v overlying the projecting ends of flanges 141. In. the oscillating movement of the yokes,

flanges 141 move tween plates 142 and -clips 144tan`d the inner ends lof the yokes are thus additionally braced and .guidedI -and disalinement of the yokes and of their trunnionsis resisted. Located on each end of each shaft 18 is aguide sleeve 29 '(see especially Figures 13 and 14), considerable clearance being provided between the shaftend and the outer `end of the sleeve. Each sleeve has parallel, vertical, `flat faces 29,

. and from each of these faces extends a trunf nion 29". The trunnions fit in bearing holes in slide blocks 29, and the blocks have flat verticalfaces arranged to slide against inner faces 9il Aof the vertical side members of the corresponding vertical'guides 7 or 9. The blocks also have flanges 2,9d engaging the front'and rear edges 9b of the guides. As the shaft ends move up and'down in the pivotal movements of the tractor frames, slide blocks 29c move vertically up anddown on the vertical guide members; trunnions 29b rotate slightly in their sockets, and the shaft .ends move somewhat in and out, in sleeves 29; and thus the necessary vertical oscillation is freely permitted, and lateral movement of -the ends of the tractor frames is effectively resisted.

The construction described is such that each tractor frame, comprising the truss 12, yoke .15 and braces 16, is an operative unit which may oscillate in the vertical plane of its shaft 18 to the extent permitted by the guides 7 and 9, the center of oscil-4 lation being the axis of trunnions 22 and 25. In this movement the guide sleeves 29 move up and down in guides 7 and 9, and the guides effectively brace the/tractor frame and the parts that it carries, against lateral movement. The tractor frame is at the same time effectively braced against any rotative movement about its shaft axis by the widely separated points of support afforded by thel trunnions.

The tractor drums D are mounted on drum shafts 18. The drum structure on each shaft may be .considered an operative unit,

but preferably this structure is separated somewhere near mid length of the shaft, and there are, in av preferred embodiment as shown, two tractor drums on each of the shafts 18, and usually the forward and rear drums on each shaft are of similar structure respects, but preferably they also differ in certain respects and the forward and rear drums will therefore be described with considerable particularity.

The forward drum 35 of each of the tractor units is in the form of a convex cone or approximate conoid, cut off only a short distance from thetip so that its surface 37 curves gradually inward from .a point 38 near the rear end to the front end of the drum. Helical flanges or ribs 39 are secured on the rear portion of the drum surface and there is a relatively large number of these ribs arranged at a rather steep pitch-angle so that several of the ribs are always in contact with the snow surface. The ribs 39 are of `moderate depth in a' radial direction from the shaft so that their front and rear faces in contact with snow at any time, even when thetractorsare sunk deep in soft snow,`are not of sufficient area to impose an undue frictional load on the motor, and at the Sametime in packed snow, where the drums do not sink into the and shape in many snow surface 'to any great extent, the ribs length, of this zone of driving ribs may be The fore drum, extending the rib zone to the varied to suit different conditions. 'ward -portion 40 .of th from the frontend of front end of the drum is finished smooth,

and has only a sliding Contact with the snow surfaces without propulsive effect. lAs the drum is driven forward bythe engagement of the ribs with lthe snow body, the smooth ,conical forward end of the drum presses or irons down loose snow or rides u easily and smoothly overpharder snow and) lumps. In the case of soft snow the forward portion of the drum thus forms a channel for t-he rearward `ribbed or driving portion, and

the ribs in effect engage vwith a trough formed in the snow body by the drum and affording. ample driving contact for the vehicle and for a trailer load. The surface of the drum from a point near the rear end of the ribbed surface is curved more sharply inward toward the shaft, providing a relatively, contact surface 41, presented to the' snow bodywhenthe tractory drum moves backward.

The rear drum 36 is in general similar to the front drum just described. It has a relatively sharply rounded front edge portion 42, similar to the rounded rear edge portion 41 of the front drum. It is provided with helical ribs 43 arranged substantially as in the case of the front drum.

more steeply upwardly incline'dv internato Between the ribbedportion and the rear end of drum 36 is a smooth portion V44 similar lto the smooth portion 37 of drum 35', but in the present embodiment of the invention, somewhat shorter. The peripheral surface of drum 36 is in the form of a convex cone or conoid, cut off at a greater distance fromits point than in the case of drum 35. ln a preferred construction the total length 0I' drum 36 is less than that of drum 35 and this difference in length is mainly taken care of in the shortening of the smooth rear portion 44. A gradual upward curvature of the lower smooth surface ofthe drum provides for pressing down so-ft snow and riding over lumps when the vehicle'y is backed, as in the case of drum 35, when the vehicle is driven forward; but since backing is .relatively infrequent the inward curvature of the rear part of drum 36 need not be carried to the same extent, in some cases,

v as in the case of drum 35. By considering the combined action of the two drums as the vehiclegoes forward or backward itv will be understood that the moderate rounded curvature of the adjacent ends of the two drums is sufficient to smooth down or ride over any irregularities that may remain in or any loose snow or lumps that may fall into, the path made by one drum after its passage and before the rounded end 41 or 42 of the other drum reaches the same point in the tractor path.

Considering the twotractors' on each shaft as an operative unit, it will be noted that the surface curvature frlom the forward. end of thel front tractor to the rear end of the reartractor is substantially continuous,

p the front tractor andthe front end ofthe rear tractor. The general continuous curvature from one end to the other of the two tractor drums constituting a tractorl unit may be a uniform curve or arp, or the forni of the curve may preferably 1n some cases be varied so that near the front end of the frognt drum 35 and the rear end of the rear drinn 36 the radius of the curve is shortened.

shaft axis the approximate form of a runner?` with upwardly curved ends; so that if the drums were pushed forward without rotation they would act substantially as runners and slide up easily over 'the softsnow 4or obv structions, in either direction of movement.

Approximately the same effect in ridingover the snow surfaces is obtained when the machine is driven forward by the rotation of the drums, a dierent linear portion of the drum` surface acting at each moment as the principal snow engaging or runner surface of the drum. Describing the contour of the tractor drums in another way, their surfaces in planes of the axis are defined by a continuous, substantially curved, line extending substantially from the front end of one drumy to the rear end of the other. The curvature of certain portions of the surfaces, usually near-the larger ends of the drums, may be decreased to such an extent that, as in the present case, certain portions of the drum surfaces are practically straight or cylindrical and 'these approximately straight or cylindrical portions are usually included in the areas of the drums which are provided with the driving ribs.

The tractor drums are of sufficiently great diameter and length to provide adequate' structures of this class. fll`he depth of the' driving ribs is small in relation to the diameter of the drums. By this arrangement ade-- quatedriving contact\ is provided without appreciable' tendency to c ut `deeply into soft sno'w bodies, or to waste power in the attempt to rotate deep driving flanges having a large area of snow contact, since the arca of the drums 1s suficlent under fall circumstances to support the drums and the vehicle to prevent the driving Aribs fro/n1 cutting or digging away the snow in the channel formed by the drums, sufficientlyA to cause the drums to sink into their channels to an undesirable extent, comparable, for example, `to the action of wheeled tractors, whose peripheral'cleats under a very heavy driving load, and on soft ground, will,fin" many cases simplyl dig a hole 'into which the. wheels sink until the chassis structure strikes the ground. lln my invention^such a 'burrowing action is avoided by the ample supportatforded by the drums.

l'-llhe detail construction!- o fL the tractor' drums may vary greatly, but the form shown his desirable and preferred in some cases. Figure v6 shows a typical drum in section.

Suitably spaced apart on the drive shaft 18 l force the shell, as, for example, by means of 'a number of hoops 121 of convenient cro section secured to the inner face of the shell. Some of these hoops may be conveniently of 4T-section, as shown, and others, such as the forward hoop 122, may conveniently be of Lsection to accommodate more easily the angle of the shell near its smaller end. At one end, such as the large end, the shell may terminate in an aperture 123. This end of the shell may be. connected to fiange 11.8 of sleeve 116 by an end plate 124 bolted to the. shell material aboutv aperture 123 and also bolted to the fiange, and this end plate may be dished inwardly as shown, to provide greater stiffness. The other end of the shell may be similarly connected to the shaft, especially in the case of the rear drums 36, where the diameter of the smaller end of the drumis quite large, or otherwise the shell material may be brought down to overlap flange 118 and vdirectly bolted to it, as shown in Figure 6.

The form of'. the driving ribs may vary greatly as previously indicated. One simple cross sectional form is shownin Figure 6. Figure 12 shows another form of driving rib, preferred in some cases. In this form the 'ribs 130 have the general cross sectional form ofl a modified T-rail, comprising a base 131 secured to the outersurface of the drum, a web 132 and an enlarged head133 of approximately circular cross section. Figure 12 shows the tractor drum resting on a hard snow surface H. -The 'ball heads 133 i of the driving ribs cut into the surface more l tact of the lower and rearward portion ofl or less, depending on the weight, imposedl the ball head 133. -Thus the frictional contact of the rib with the snow body is very much reduced with a corresponding decrease in frictional resistance and gain in speed or draw-bar pull. This construction also avoids a difliculty encountered in connection with,

driving ribs of substantially flat radial form, due to the fact that when such blades are arranged helically, the curvature of they -bladeat its baseis different from the curvature at the periphery, in accordance with the well known variations inl curvature of `spiral planes. It lhas been found in practice, that flat blades of this sort cannot be feasibly given the exact lcurvature required, there-1' l.sult being that the blades bear unevenly Nat different point'sjin'their travel, against the ing of the snow kerf, accompanied by undesirably great friction and resistance to rotation of he blades. The enlarged heads 133 of the "I lades just described 'cut a snow groove or kerf Wider than the thickness of the blade-webs, and consequently variations in helical curvature ofthe blade-web are of little or no consequence, since the sides of the web ordinarily do not have any` sliding contact with the snow surface.

The heads 133 ofthe driving ribs are not necessarily of the round cross section but may when necessary or desirable be made with relatively sharpened peripheries for example of approximately heart-shaped cross section so that the outer edges of the ribs will bite into hard ice with satisfactory driving effect. I

A sprocket 50 is fixed on eachtractor shaft 18 between bearings 17. Near the inner end of ,each yoke its side members are provided with upward extensions 51 `for the connection of sprocket frames 52. Each of these frames has side members 53 provided with slots 54, and bolts 55 passing throughthe sl-ots and holes in yoke extensions 51 secure the sprocket frames to the yokes adjustably toward and from sprockets 50. The sprocket frames, 52 are provided with bearings 56 vand in these bearings sprocket shafts 57 are mounted. On each shaft between the bearings is a small sprocket 58 connected to the corresponding large sprocket 50 by la chain 59. The adjustment of sprocket frames 52, to regulate the ti htness of the chain is conveniently provi ed for by a set screw 59a passing through a bracket 60a carried by yoke 15 and bearing against cross member 52a of the sprocket frame. A. lock nutv60 is provided for the screw 59a. When the nuts of bolts 55 are loosened the sprocket frame may be4 moved to left or right, as viewed in Figure 4, by turning screw 59 and the adjustment thus secured may be made permanent bv setting up the nuts or bolts r55. The described mounting and ad justment of the small sprockets is representative of other arrangements that may be used.

Tractor shafts 18 are rotatively supported in their frames on suitable bearings in bearing casings 17, 19 and 20,y abovementioned. The radial support of the shaft may be on typical radial ball bearings 17 and 20, Figure 13, or bearings of any other suitable form. In addition, to take the end thrust of the shafts, one or more thrust bearings, such as ball thrust bearings 17"--20h are usually also provided, and these may be associated with the radial bearings as shown.

`For Example, ball thrust 20b is located against the inner ring of bearing 20" in l o casing 20 and the outer ring of the thrust rearward side "of the kerf formed by them, Ab resulting in undesirable distortion or widen-` caring is engagedbyh the inwardly projecting .flange o an adjusting thimble 20c screwed into the casing and secured by a locking member d, as usual in bearings of this type. Similarly, thrust bearings 17b in casings 17 may be adjusted by thimbles 17. By suitable adjustment of the thrust bearings, the end thrust of the shaft in either direction may be taken up by two of these bearings and is so distributed between yoke 15 and the ends of longitudinal truss 12. Where only a single thrust bearing near each end of a shaft, such as bearings 20, is provided, the thrust in either direction is taken, by one of these bearings and transferred to the corresponding end of longitudinal truss 12 and from it to the main frame through the yoke trunnions. n.

Near the rear end of the machine `a gear casing 61 is secured to the main frame.

f Casing 61 encloses meshed gears 62 and 63,

carried by shafts 64 and 65, respectively,` and these shafts are. mounted in bearin s 66 located in the front and rear walls o the casing. The shafts extend through the front wall of the casingV and are there provided with universal joints 67 and 68 respectively, the casing also enclosing a pinion 69, carried by a shaft 70, mounted'in suitable bearings and extending through the front wall of the casing. F The pinion 69 engages with either of the large gears (in the present instance with gear 63) and the pinion axis is set slightly to one side of the longitudinal frame center, to .permit this engagement without conict with vgear 62. A universal joint 71 is mounted on 'the forward end of shaft 70.' A shaft 72, which is the driven shaft of the. change-speed gearing, extends through the rear wall of gear casing Gr, and is provided with a universal joint 73. This universal joint is connected with universal joint 71- of the rear drive pinion by a propeller shaft 74 which is arranged at a slight angle to the longitudinal axis of the vehicle to accommodate the offset position of pinion shaft 70. A propeller shaft 75 is connected -to universal joint 67 of transmission gear 62 and extends forward at a moderate angle and is connected to the rear end of shaft 57 of the right hand tractor sprocket 58 by a universal joint 76. Similarly a propeller shaft 77 connects universal joint L68 of transmission gear 63 with sprocket shaft 57 of the left hand tractor unit, through a universal joint 78. When it is foundnecessary or desirable any or .all of the propeller shafts may be provided with asli joint, as indicated at 79, in propeller sha 't'75. 'j

- The driving parts and connections` described operate as follows: When the motor rotates in the usual right-hand direction, as

viewed from the front, and the main clutch" is engaged, with'a suitable forwarddrive gear combination 1n engagement in the gear box, the propeller shaft 74 drives :pinion 69 in a left-hand direction as viewed from lthe Ain rear in Figure 3. The pinion drives gear- 63 in a right-hand direction'and gear`62 in the opposite direction. These gears through propeller shafts 75 and 77 and the associated universal joints drive the small "tractor sprockets in the same respective directions as the gears, that is, sprocket 58 of the righthand tractor unit, as viewed in Figure 4, has a left-handy rotation and the similar sprocket at the left-hand unit has a righthand direction. The corresponding large sprockets of the tractor units and the tractor` drums 66 are thus correspondingly driven7 that is, the right-hand drums have a lefthand rotation and the left-hand drums have a right-hand rotation, as viewed from the The change-speed gearing. provides a suit- .able number of forward drives of suitable ratios and at least one reverse drive. lin addition to conveniently providing for the transmission of power from a power plant, arranged in convenient position on the main or chassis frame, to tractor units, at a point considerably forward from the rear end of the vehicle, the transmission mechanism de-I scribed 'also affords opportunity to introduce into the drive line a number of speed reductions, and the amount of reduction as between the driven member of the change-gear box and the tractor shafts may be considerabl varied to meet diderent conditions by suita lyvarying the sizes of the different gears and sprockets in the transmission line beyond the change-gear box. ylixfplicitly,

the diameter of pinion 69 in relation to that of gears 62 and 63, may be varied, and the diameter of sprocketsl 58 in relation to that of sprockets 50 may be varied, to determine the amount of speed reduction at each of those points; -or a reduction at either point maybe avoided or an increase of speed may .even be provided by suitably proportioning 11o .drums of each tractor unit provides' advan- 12o tageously for the location of the tractor driv- 'g means in line with the pivotal axis of the .tractor units; i

The mainlower member or beam 4 of the rigid frame structure extends forward lfrom 125 its point of connection withfchassis frame F 'and is conveniently curved downward somewhat at 80 and again straightened out at 81and is provided with a`yoke or clevis '82 to receive a transverse member 83 which 130 sprin is the mainframe member of the steering structure and may be identiied, for convenience, as a steering cross-beam. The cross beam is connected to longitudinal beam 4 by a bolt 84 passing through the sides of the clevis 82 and engaging in a suitable bearing formed in the cross beam. Diagonal braces 85 are connected to the cross beam nearfitsouter ends and are also connected to beam 4 by means of a suitable socket 86, Figure 1. The cross beam is provided at each end with a steering head or sleeve 87 and each of these provides a bearing for a steeringspindle 88. The lower end of each steering spindle is formed into a yoke or clevis 89 embracing one of the steeringrunners 90. A bolt 91 passes through the sides of clevisl 89 and through a bearing in the runner to permit the runner to osclllate in a'vertical plane.- Each steering spindle is also provided with a longitudinal cross piece 92. Forward of the steering spindle the runner is provided with va spring rod 93 pivoted to the runner 94 and passing through a holewin cross piece 92. Back of the steerin g spindle the runner is also provided with a :spring 'rod 95 pivoted at 96- and passing through a similar hole in the cross piece. A spring 97 is mounted on each spring rod between the runner and the cross piece. Preferably the forward spring rod' and are located nearer to' the steering spind e than the rear spring device.f The form of the runners may vary considerably,

but in a preferred arrangement the tread surface 98 is curved throughout its length, the curvature increasingv toward the front .and to a smaller degree toward the rear, and being'relatively moderate at a point below the steering spindle, The runner treads are preferablyprovided with downwardly extending flanges 99 which provide sufficient lateral bearing engagement with the snow ro er steering action. The lower edges o tliiese flanges may be suitably sharpened to properly cut into hard snow or ice.

`. The describedsteering sti'uctureis such that on encountering irregularities inthe snow surface, the lfrontor rear end .of the runner ,will v ride over themv easily fand smoothly. Considering the usual direction vof travel, forward, upon encountering a lhummock, the upwardly curved tread of the runner.l gradually rides up over it, and ing doing'so the runner pivots in clevis 89 and.

v transferred to a point directly under the forward spring 97 is compressed, serving to yieldably transfer 'a part 'of the load to the steering spindle. As the runner goes ferward over the obstacle the load is gradually spindle, and further movementthe runner tilts in the other direction, with accompanyng compression ofspring 97 until the obstacle is passed. The greater distance .of

rear spring 97 from the steering spindle gives this spring a greater leverage effect upon the runner than that of the `forward spring and, therefore, the runner is able to tilt up to ride over an obstacle with relative ease, but supports the front end of the vehicle through the runner with relatively greater firmness as the steering spindle passes beyond the obstacle. At the same time, owing to the pivotal connection of the cross beam 83 with beam 4, either runner as a whole moves un or down about the pivot center 84 in accordance with the general ground level at either side of the vehicle.

In addition to providing for easily surmounting obstacles, the convex tread of the steering lrunners permits 'them to be quite easily turned from side to side in steering, especially in soft snow, since the weight carried by the runner is borne upon a more or less restricted segment of the curved tread.

A steering column 100 carrying a hand wheel 101 is mounted in the chassis frame in the usual way. The column termmates at its lower end in a steering-gear casing 102,'

having a steering arm 103, as usual in motor vehicles, exceptf that this larm is turned upward, instead of dependin from its 'shaft 104. This arrangement o steering avoids interfering with the longitudinal clearance' space betwieen the tractor umts, previously mentioned, b steering arms or other parts extending ownward into this space, as would occur in the ordinary arrangement of such parts, and also prevents obstruction t`o the y u ward movements of theadjacent drum. ach steering spindle 88 of the runners 90 is provided with an arm 105 and these are connected by a crosslink 106. One of the spindles, in this case the left-hand spindle, is also provided with va steering arm 107, all as usual in motor vehicles.N Owing to the considerable elevation loffthel chassis frame above the runners, a special arrangements of parts is usually necessary to properly connect steering arms 103 and 107. This arrangement comprises in this embodiment, a lever -108 fulcrumed at 109 on a bracket 110 carried by chassis frame F. A'drag link 111 convnects the upper end of lever 1,08 with steering arm 103, and another drag link 112 connects the lower end of lever 108 with-the end of steering arm 107. Preferabl the steering arms 103 and 107 are rovidedwith ball ends and the upper and yower ends ofy lever 108 are alsoprovided with ball ends, and these ball ends cooperate with suitable sockets in the ends of the drag, links, as usual in motor vehicles. The movement fof steering arin 108 is transferred by lever 108 from drag link 111 to link '112, and so to the 'steering' runners in an obvious manner. From: the escription -of the tractor and parts naar@ runner mountin it is now apparent that the weight of t e main frame of the vehicle is supported, considering the longitudinaldistribution of weight, at two points,

namely theV axis of trunnions 22 and 25 and the center of'steering cross beamv 83. 'lF-he greater partof the weight is borne b y the `Atractors and a suitable, smaller portlon 1s `borne' by' the steering runners, suiiclent to insure proper steering enga-gement with the snow surface. Considering the lateral dlstribution of the wei ht, it is evident that it is distributed` equa ly to the two tractor .units 'through the cross beam' 2, yokes 15 bility of the tractors, which causes the posi-f tion of the pivot center to be at all tunes, roughly speaking, the average of the elevation of the two ends of the unit. Pivotal connection of the front end of beam lwith the steering cross beam readily permits the tilting of the main frame in response to the positioning of the' tractor units, regardless of the position of the steering runners and conversely either of the runners may risev or fall as a whole as they encounter lumps or depressions without tilting the main frame or imparting torsional strains to it. Otherwise expressed, the support of the main frame is on a transverse axis, which is the axis of the trunnions, and a point, whichis the lpivot axisof the steering cross beam, constituting what is commonly termed in the motor `vehicle art, a three point support.

Figures 10, and 11 show diagrammatically the accommodation of the tractor drums and of the steering runners to different conformations of snow surfaces. ln these figures both drums are shown in contact with the sides. of a hollow, and it is evident from these diagrams that a considerable longitudinal area of both drums will always engage with the snow surface in spite of irregularities, because of the longitudinal curvature of the drums and their pivotal mounting in the main frame. Each tractor unit tilts or rocks in passing over irregular surfaces in very much the same manner as the steering runners, whose action has been described. If, in going forward, the front tractor drum encounters a slight rise, this strikes the drum surface at a point near the ribbed portion and the front end of the tractor is tilted. upward only slightly and the lmain contact of the rear drum shifts to a oint near the rear end of its ribbed belt. uch a slight rise or obstruction corresponds practically to a moderately curved surface, such as is shown in Figures l() and 11, with which a relatively large part of both tractor drums of a unit will engage.- If the obstruction or elevation is higher, corresponding to a greater curvature of snow surface, the principal Contact with the` drum surfaces will shift toward the outer ends of the drums and on irst encountering this obstacle the front end of the tractor unit will tilt up more sharply than in the previous case. -lln any case a substantial part of the under surface of each tractor drum maintains adequate supporting and driving contact with the snow surface. ln this way adequate tractive contact is always maintained `without either localizing pressure unduly on parts of the drum surfaces, creating undue strains or materially decreasing the driving capacity of the drums.

llt is evident from the detail description ofthe structure that adequate provision is made to resist and adequately distribute strains, and particularly strains applied to, the movabletractor, units. In going for-- ward, the forward portions of the front tractor drums frequently have angular contact with projections whichy tend to ymove tllile front ends of the tractor frames later? a y. guide-sleeve, slide-blocks .29c with the vertical front guide members 7, which transfer this lateral strain to the main trame. Similarly any lateral deflection of the rear end of the tractor frame is resisted by vertical guides 9. A part of the lateral strain is .transferred through the shafts to yokes andv through the yoke trunnions to longitudinal beam 4 and transverse beam 3 which are braced by the main frame. The vertical load on the tractor shafts and added strain caused by vertical tilting is transferred to longitudinal truss 12 at its ends and at the center through diagonal braces 16. Strains applied laterally to the front and rear drum ends tend also to twist the yokes 15 out of their transverse horizontal position. This twisting is resisted by brace arms 140 and their guides. yStrains often occur which tend to move the tractor units outwardly away from the longitudinal axis of the machine. This occurs, for instance, when there is a ridge in the roadway, the sides of which. are straddled by the drums of the respective tractor units. Such strains tend to move the yokes 15 partly outward, and are resisted by the inner trunnion bearings 24 engaging heads 27 of the trunnion bolt 25, as well as by the outer trunnion connectionn ofthe yokes with cross beam 2. 'Further analysis of the strains and lstresses which are applied to the tractors will show This is resisted by engagement of that the arrangement provided takes care of all of them properly and distributesl the strains to several parts of the tractor frames and their diferent connections with' the main frame, and so to several parts' of the main frame and thus undue strain on any one part is revented. Y 'l nd thrust on thedri'ving shafts 18 caused mainly by the driving reaction'is taken "up by the thrust bearings 17", 20, land distributed to the ends 13,14, of 'longitudinal truss 12 and to yokes 15 and from the yokes is transferred to themain frame Ithrough the trunnions and cross beam 2.

Figures 3 and 4 show-'most clearly that the arrangement of frame and driving parts provides a wide and high longitudinal clearance space throughout: the length ofthe machine between the tractor drums. Ilhe uper llimit of this spaceis substantially degned by the Vunder sides of beam 4, cross braces 11 and `1O,and yokes 15. The lower stretches of drive chains 59 passoutside of the limits ofthis longitudinal clearance.

space, as clearly shown in Figue'4. Even when the tractor drums sink deep into soft snow, the centralridge between the channels formed by the drums is accommodated 'in this clear space Without. any parts of the vframe dragging on the snow surface, except in the most exceptional cases.

What Iclaim is: 1. In' a snow motor vehlcle, a main frame carrying a motor, change speed gearing and control devices, a -tractor comprising two.

substantially conoidal drums of large diameter and s'uiicient' length to 'support the drums andthe vehicle properly in soft deep snow, the drums being'inaxial alinement with their larger endsfadjacent,.o`ne of the drums having a largel part of its surface extending away" yfromt the. smaller end smooth, a large remaining'p'artof its surface being provided y'with helical driving ribs, a shaft rotatably supporting the drums, an oscillatable connection between the trac.- tor and the main frame, and a driving con-v nection between the changespeed `gearing and the 'drum shaft.v

` 2. In a snow motor vehicle,l a main frame carrying amotor, change speed gearing and control devices, a ytractor comprising two substantially conoidal drums of large diameter and1sucient `length to support the drums and :the -vehicle properly in soft deep snow, the drums being inaxial alinement with their larger ends adjacent, one :of the drums having a large part of its surface exf y tendingaway'lromthe smaller end'smooth,

a large `remaining -parto'f its surface being provided ywith helical'driving ribsgfthe sur- Yfaces of the"drul'l'1sl approaching'ftheiradjacent .ends being-'rounded inward relatively sharply, afi-shaft rotatably supporting the drums, yan oscillatable connection between the drum structure and the main frame, and a driving connection between the change speed gearing on the main frame and tie drum shaft.

3. Ina snow motor Vehicle, a main frame carrying a motor, change speed gearing and control devices, a tractor comprising two substantially conoidal drums of large diameter and sufficient length to support the drums and the vehicle properly in soft deep snow, the' drums being in axial alinement with their larger ends adjacent, one ofthe drums having a large part of its surface extending away from the smaller end smooth, a large remaining part of its `surface being provided v`with a'plurality of shallow helical driving' ribs, a shaft rotatably supporting the drums, an -oscillatable connection between the tractor andthe main frame, and a driving connection between the change speed gearing and the drumn shaft.

4. Ina snow motor vehicle, a main frame carrying a motor, change speed gearing and control devices, a tractor comprising two substantiall conoidal drums of large diameter andsu cient length to support the drums and thc/vehicle properly in soft deep snow, the drums being in axial alinement with their larger ends adjacent, one of the drums having a large part 'of its surface extending away from the smaller end smooth, a large remaining part of its surface bein provided with a plurality of shallow helica drivi'ng ribs, the surfaces of the drums approaching their adjacent ends being rounded inward relatively sharply, a shaft rotatably supporting the drums, an oscillatable con'- nection between the drum structure and the main frame, and a driving connection between the change speed gearing on the main frame and the drum shaft.

5. In'a snow motor vehicle, a main frame carrying a motor, driving mechanism and controlling devices, and-a tractor structure oscillatably connected to the main frame and including a rotatable shaft, two separated conoidal tractor drums mounted on the shaft,rwith the larger ends of the vdrums l adjacent, each drum having alarge smooth surface yextending from its smallery end toward the' other end, each drum having a zone provided with helical driving ribs arranged With a steep pitch angle, thevadjacent lends of the drumshavlng an'accentu ated inwardcurvature; and a drivingconnection between the drum shaft and the driving mechanism on the main frame.`

6. In a snow motor vehicle, a main frame carrying a motor, clutch and transmission I mechanism, a tractor frame oscillatably connected to themain frame, a drive shaftin the tractor frame, two separated conoidal tractor drums on4 the'shaft with their larger ends adjacent, each drum having an extensive smooth surface adjacent to its smaller more end and an extensive surface adjacent to its larger end provided with helical driving ribs, and av driving element on the shaft -betwn the drums, and transmission mechanism connecting' said driving element with the transmission. mechanism on the main frame.

7. ln a snow motor vehicle, a main frame carrying a motor and transmimion mecha-l nism, a tractor frame oscillatably connected -to the main frame on a transverse horizonthe vehicle in soft deep snow, a driving member on the shaft between the drums approximately in line with the osclllating axis of the tractor frame, and a driving connection between said member and the main frame transmission mechanism, adapted to conform to the relative movement of the tractor frame and main frame. i

8. ln a snow motor vehicle, a main frame carrying a motor and control devices, a

tractor frame connected to oscillate-verti cally at a point substantially near its center to the main frame, va shaft rotatably mounted in the Vtractor frame, oonoidal tractor drums on said shaft of sufficient diameter and length to support them and `the vehicle in ysoft deep snow, one of the drumgs having a smooth surface extending from its smaller end approximately to a point where the longitudinal lower surface of the drum is'approximately parallel to the normal snow surface, a large part of the length of the d surface rearward of the smooth surface being provided with a plurality of shallow helical driving ribs, the

other drum having its surface for a considerable length provided with a plurality of similar driving ribs, means for guiding the tractor frame in its oscillating movement and, preventing lateral deflection of said frame, and -a driving connection between said shaft andl the mlotor.

9. ln asnow motor vehicle, a drum shaft, a pair of spaced conoidal tractor drums on lthe shaft, one of the drums having a large smooth surface near its smaller-end and a large surface provided with a plurality of helical driving ribs, means for bracing the shaft in vertical and horizontal planes, ay vmain frame, an oscillating connection between the main fre" and the tractor shaft, andmeans for guiding the oscillation of the tractor shaft and drums relative to the main frame and preventing lateral dedect-ion of the tractor shaft.

10. ln a snow motor vehicle, a main frame, a motor and speed-change and controlling mechanism thereon, a tractor rstructure comprising a longitudinal truss, a transverse yoke havin bearin for an intermediate portion o the sha a vertical brace connecting the yoke and truss, a tractor drum of large diameter on the shaft between the yoke and one end of the truss, said drum having an extensive curved smooth peripheral surface and an extensive peripheral surface provided with helical driving ribs, another tractor drum of large diameter on the shaft lmtween the yoke and the other end of the truss, and having an extensive surface provided with a plurality of shallow helical driving ribs, a drive member on the shaft within said yoke, a second drive member carried by the yoke near its inner end, a driving connection ltween the two members, means for adjusting the second drive member toward and from the shaft, means carried lby the main frame providing an oscillatin port for said yoke in a transverse horlzontal .axis ofA .the vehicle, guide means inter- 'mediate the main' frame and the ends of the tractor structure to guide the latter inrits vertical oscillations and prevent lateral deflection, and a driving connection between the second drive member and the speedchange mechanism on the main frame, including means to accommodate thev oscillating movement of the yoke.

Sllp- 4 4'11. In a snow motor vehicle,a main frame,

two tractor frames movably connected to the main frame, one at each side, a conoidal tractor drum-located in each tractor'frame and having a smooth surface extending from the smaller end a considerable distance toe Ward the larger end and a plurality of shallow helical driving ribs arranged on the drum surface between the smooth portion and the larger end of thedrum, the drum being of sucient diameter and length to support the vehicle in deep, soft snow, and means lfor rotating the drum.

12. ln a snow motor vehicle, a main frame carrying a motor and power transmission mechanlsm, two tractor frames oscillatably connected tothe main frame, one at each side, a tractor drum rotatably mounted in each tractor frame, the drum having a smaller and a larger end and its surface being convexly curved from the smaller end to a point near the larger end, the surface being smooth from the smaller end for -a ing of sufficient diameter and length to support itself and the vehicle in deep soft snow, and driving connections between. the

`tractor drums and the' transmission mechanism onthe main-frame. v L 13; In a snow` motor vehicle, a main frame carrying a motor, change-speed gearing and control devices, twok tractors, one located at each side of the mainl frame and each com- Y prising two substantially conoidal drumsof I drum shafts.

^ 14. In a snow motor vehicle, agmain frame carrying a motor, change-speed gearing and control devices, two tractors,` each comprlsing two substantiallyV conoidal drums of.V

llarge diameter and suiiicient length A to sup), port the drums and the vehicle properly soft deep snow, the drums being in axial alineinent with their larger ends adjacent, one of the drums having a large part of its surface extending away from the smaller endsmooth, a large remaining part of its surface bein provided with a plurality of helical drivin ribs, the surfaces of the drums approacing their adjacent ends being rounded inwardly relatively sharply, a shaft rotatably supporting the drums and an oscillatable connection between the drum structure and the main frame and Adriving connections between the` change-speed gearing Y and the drum shaft.

15." Ina snow motor vehicle, a` main frame carryin a. motor, driving mechanism and controlling devices, two tractorstructures oscillatably connected to the main frame, one at each side of the main frame, and including a rotatable shaft, two separated -conoidal tractor drums mounted on the shaft, with the larger ends of the drums adjacent, each drum having a large smooth surfaceextending from its smaller end toward .the other end, each drum having a l 4'zone provided with a plurality of helical driving ribs arranged with "a steep pitch Aangle, the adjacent ends of the drums hav- :ing

l Van accentuated inward curvature, and driving connections between the drum shafts and the drivingmechanism onnthe mairr frame. Y l I 16. In a snow motor vehicle, a main frame carryin a motor, clutch and transmission mechanism, two tractor frames oscillatably connected tothe main frame, one at each side of the mainframe, each tractor frame .comprising a drive shaft, two separated. conoidal tractor drums on the shaft with their larger ends adjacent, each drum hav- .ing an extensive smooth surface adjacent to its. smaller end and an extensive surface adj acent'to its larger end provided with a plurality of helical driving ribs, a driving element on the shaft between the drums, and transmission mechanism connecting said driving elements with the transmission Vmechanism on the main frame.

17. In a. snow motor vehicle, a main frame carrying a motor and transmission mechanism, two tractor frames located at opposite sides of the main frame and each oscillatably connected tothe main frame on a transverse horizontal axis at a point substantially near the longitudinal center of the tractor frame, a shaft rotatably mounted in each tractor frame, two' spaced tractor drums on each shaft, the drums having peripheral surfaces convexly curved longitudinally, a large part of the surface of one of the drums being smooth and another part of its surface being provided with a plurality of helical driving ribs, the drums being of relatively large diameter and'- length sufficient to support them and the vehicle in soft, deep snow, a driving member on each shaft between the drums approximately in line with the oscillating axis of the tractor frame, and'drrving connections between said driving members and the main frame, and transmission mechanism adapted to conform to the relative movement of the tractor frame and main frame. l

18. In a snow motor vehicle, a main frame, carrying a motor and control devices, two tractor frames, one at each side of the main frame and connected to oscillate vertically at a point substantiall near its center to the main frame, a sha t rotatably mounted in each tractor frame, s aced conoidal drums on each shaft of su ient diameter and length to support them and the vehicle in deep, soft snow, one of the drums on each Shaft having a smooth periphery extending from its smaller end to about the middle of the drum, and having its surface extending from that point to a point near the larger end of the drum provided with a plurality of helical driving ribs, the other drum on each shaft having its surface provided with a plurality of similar driving ribs', means for guiding .the tractor frames in their oscillating movement and preventing lateral deflection of the frames, and driving connections between'said shafts and the motor. 19:. In a snow 'motor vehicle, a pair of parallel drum shafts, a pair of s aced conoidal tractor drums on each sha t, one of the drums of each pair having a lar smooth surface near its smaller end and a ar surface provided withx'a. plurality of siillow helical driving ribs, means for bracing each of the shafts in vertical and horizontal planes, a. main frame located between and above the shafts, an oscillating connection between the main frame and each of the shafts, and means for guiding the oscillations of the tractor shafts and drums relative to the main frame and preventing lateral deflection of the tractor shafts.

20. In a snow motor vehicle, a main frame, a motor, change speed gearing and control devices located thereon, a tractor unit at each side of the main frame, each tractor unit comprising a frame, a longitudinal shaft mounted in bearings in the frame, two tractor drums located on the shaft and spaced apart from each other, the. general longitudinal contour ofthe drums being'l a curve presenting a considerably upwa-rdly-inclined angle to the snow surface at the front end of the forward drum and at the rear end of the rear drum, approximately half of the -forward surface of the forward drum being smooth and a principal part of the remaining surface of the drum'being provided with helical driving ribs, a considerable part of the rearward surface of the rear drum being smooth and a large part of the remaining, surface of the drum being provided with a plurality of shallow helical driving ribs, the

peripheral surfaces of the adjacent ends of the two drums being curved inward toward the shaft to present a curvedly-inclined surface to the snow surface in either direction of movement of the vehicle, a ydriving member on each shaft between the drums, a trans- -verse member forming part of thev tractor frame and connected oscillatably in a transverse horizontal axis with the main frame, the oscillation axes of the two tractor frames being substantially coincident, a second driving member located near the inner end of each of said transverse members, said second driving members being each connected to the first mentioned driving member of its tractor unit, a gear casing near the rear end of the main frame, transmission gea-ring therein, a flexible driving connection from a. part of said gearing to one of said second driving members, a flexible-driving connection from another part of said gearing to the other of said second driving members, and a driving connection from said change-speed gearing to a part of the transmission gearing in said rear gear casing.

21. In a snow motor vehicle, a main frame having a forwardextensioma tractor frame at each side of the main frame and Hexibly connected to it, a vtractor drum in each tractor frame of large diameter and suilicient length to support the vehicle in soft, deep snow, the tractor drums having surfaces convexly curved longitudinally, a large part of the peripheral surface of each drumbeing smooth and a large part of the remaining surface of each drum being provided with a plurality of helical driving ribs', means for -driving the drums, a steer- 1ng runner and a connectionbetween the runner and said forward extension of the main frame, said connection including means by which the runner` may be deflected laterally for steering and means by which the runner may oscillate in a vertical plane in passing over irregular surfaces,` steering mechanism on the main frame vand a connection between said steering mechanism and the runner for effecting its steering movement.

22. In a snow motor vehicle, a main frame having a forward extension, tractor drums supporting the main frame, means for driving the drums, a steering cross beam pivotally connected at its center .to said main frame extension to oscillate in a transverse vertical plane, a substantially upright steering spindle mounted in a bearing at each end of said cross beam, a steering runner pivotally connected to the lower end of each spindle to oscillate vertically, spring means to regulate the vertical oscillation of the runners, a steering arm connected to each steering spindle, a cross link connecting the arms, another steering arm connected to one of the spindles, a steering gear on the main frame, and a connection from said steering gear to the steering arm last mentioned.

23. In a snow motor vehicle, a main frame having a forward extension, tractor drums supporting the main frame, means for driving the drums, a steering cross beam pivotally connected at its center to said main frame extension to oscillate in a transverse vertical plane, a steering spindle mounted in a bearing at each end of said cross beam, a steering runner pivotally connected to the lower end of each spindle to oscillate vert1 cally, spring means to regulate the verticalV oscillation of the runners, a steeringarm connected to each steering spindle, a cross link connecting the arms, another steering arm connected to one of the spindles, a steering ear on the main frame, and a connection rom said steering gear to the steering arm last mentioned, said steering connection including a lever fulcrumed on the main frame, a drag link connecting the steering gear with Said lever and another drag link connecting said lever with said steering arm.

24:. lln a tractor drum for snow motor vehicles, a helical driving rib fixed to the drum Surface and having a peripheral port1on or head, and a relatively thin web between the head and drum surface.

25. ln a tractor drum for snow motor vehicles, a shell of circular cross section provided with helical driving ribs, the crosssectional shape of each rib being characterized by a relatively thin web and an enlarged rounded head.

26. A tractor drum for snow motor vehicles, comprising a Shaft, flanges thereon, a drum of approximately conoidal contour having its ends fixed to the flanges, and a multiplicity of helical driving ribs secured to a portion of the drum surface, leaving an extensive part of the drum surface smooth.

27. vA tractor drum for snow motor vehicles, comprising a shaft, an approximately conoidal shell having its ends secured to 'the shaft, a plurality of shallow helical driving ribs secured to a portion of the shell surface and annular reinforcements within the shell.

28. A tractor drum for snowmotor vehicles, comprising a shaft provided with flanges, an approximately conoidal shell, means securing the smaller end of the shell to one of the flanges, a plate secured to the other flange and in turn connected to the other end of the shell, and a plurality of helical driving ribs secured to a portion of the shell surface.

29.l In a snow motor vehicle, a main frame including a longitudinal beam, and a cross beam located above the longitudinal beam,

a tractor frame comprising a yoke pivotally connected to the longitudinal beam and the cross beam and lateral'brace means for the yoke comprising brace members extending aterally from the yoke at each side of its pivot connection with the longitudinal beam,

, and guide means carried by the longitudinal beam engaging the brace members and guiding them in their oscillating movement while resisting lateral deflection of the yoke.

30. In a snow motor vehicle, the combination of a longitudinal frame member, ayoke pivotally connected to the frame member, brace arms extending from the yoke, one at each side adjacent to the above connection, and guides carried by the frame member and engaging the brace arms to permit oscillation of the yoke and resist lateral deflection thereof.

31. A snow motor vehicle including axially aligned propelling drums having snowengaging surfaces principally located in a single longitudinally convex plane.

. 32. A snow motor vehicle comprising two axially alined tractor drums, the longitudinal contour of the drums being defined by a continuous curve extending substantially from the front end of one drum to the rear end of the other.

33. A snow motor vehicle comprising a drive shaft and two tractor drums thereon having their principal longitudinal surfaces defined by a continuous curved line extending from the front end of one drum to the rear end of the other.

34. A snow motor comprising a main frame, a motor, transmission mechanism, and a tractor unit comprising a longitudinal shaft, two tractor drums thereon having substantially continuously curved surfaces extending from the front end of one drum and two longitudinal tractor shafts, one arto the rear end of the other, and helically arranged driving ribs on the drums.

35. In a snow motor vehicle, a main frame, a motor and transmission mechanism ranged at each side of the vehicle, and a pair of tractor drums on each shaft, the surfaces of each pair of drums being defined by a substantially continuous curve.

36. In a snow motor vehicle, a main frame, a motor and transmission mechanism thereon, and longitudinal "tractor frames, one pivotally connected at each side of the main frame, each tractor frame car- Vrying a longitudinal shaft and a pair of tractor drums thereon, the surfaces of each pair of drums describing a substantially continuous curve to support the machine on irregular surfaces by pivotal movement of the tractor framles and simultaneous engagement of a part of the surface of each drum of each pair with the snow Surface.

37. In a snow motor vehicle, two pairs of parallel alined tractor drums having the surfaces of the drums of each pair defined by a continuous curved line extending from end to end of the pair of drums.

38. In a snow motor vehicle,`.a pair of parallel d'rum shafts, one arranged at each side of the vehicle, a pair of spaced conoidal tractor drums on each shaft, one of 4the drums of each pair having a smooth surface extending from its smaller end for a considerable distance toward its other end, and a large surface between said smooth portion and the other end of the drum provided with a plurality of separate helical driving ribs, a main frame, an oscillating connection between the main frame and each of said shafts, and means for guidin the oscillations of the tractor drums re ative to the main frame to prevent lateral deflection thereof, the drums being of sufficient diameter and length to support the vehicle in deep soft snow.

39. In a snow motor vehicle, a pair of parallel drum shafts, one arranged at each side of the vehicle, a pair of spaced conoidal tractor drums on each shaft, one of the drums of each pair having a smooth surface extending from its smaller end for a considerable distance toward its other end, and a large surface between said smooth portion and the other end of the drum provided with a plurality of separate helical driving ribs, a longitudinal truss member spanning each pair of drums, a main frame, an oscillating connection between the main frame and each of said shafts, and means for guiding the oscillations of the tractor drums relative to the main frame to prevent lateral deflection thereof, the drums being of suflicient diameter and length to support the vehicle in deep soft snow.

40. In a snow motor vehicle, a pair of par- 

